This invention relates to plugs of the type that are employable in a passage to effect the blockage of liquid therethrough, and more particularly to a nozzle plug that is capable of being used to provide a temporary liquid tight seal of the inlet nozzle and/or outlet nozzle of a steam generator of the kind that is cooperatively associated with a nuclear reactor in a conventional nuclear power generating system.
It has long been known in the prior art to employ a plug to effect the blockage of a normally open passage, when for some particular reason such action is deemed necessary. Moreover, the prior art is known to be replete with examples of various forms of plugs, which differ one from another in terms of configuration, mode of construction, etc. On the other hand, even though a multiplicity of plugs of different design exist in the prior art, there continue to arise applications wherein it would be desirable to be able to employ a plug, however, due to the peculiar nature of the application, the plugs of known design, which are presently available, are unsuitable for use therein.
One such application involves the accomplishment of the blockage of the inlet nozzle and/or the outlet nozzle of a steam generator, the latter being of the type that is suitable for employment in cooperative association with a nuclear reactor to form therewith a component part of a nuclear power generting system. The steam generator to which reference is had here may, for purposes of this discussion, be construed as constituting simply a closed shell, which has formed therein a means through which fluid enters the steam generator and another means through which fluid exits from the the steam generator. These means comprise, more specifically, an inlet nozzle and an outlet nozzle, respectively.
Periodically, there arises a need to conduct maintenance on and/or to effect minor repairs of the internal components of the steam generator. To accomplish such tasks, it is necessary for one or more persons to actually physically enter the steam generator. Ingress into and egress from the steam generator by such persons is accomplished through suitable means such as for instance a manhole, etc., that has been provided for this purpose. While such persons are working in the steam generator, it is desirable that a blockage of the inlet nozzle and the outlet nozzle of the steam generator be effected to insure that there will be no fluid flow through the steam generator, which might imperil the lives of the people working therein.
A nuclear power generating system is designed to be operative, i.e., on line, 24 hours a day, 365 days a year. Whenever the nuclear power generating system is not operating, i.e., is shut down, either as a result of a malfunction in some part of the system or in accordance with a preestablished scheduled shutdown, it is imperative that the nuclear power generating system be brought back on line as soon as possible, for economic reasons if for no other. Namely, it is very time consuming as well as expensive to take a nuclear power generating system off line particularly when it is also necessary to shut down the nuclear reactor, and then return the system to an online state.
Accordingly, it is desirable, to the extent possible, that all work either in the form of normal maintenance or minor repair work involving any of the operating components of the nuclear power generating system be done at the same time to minimize the number of times that the nuclear reactor must be shut down. Consequently, the preferred operating procedure is to strive to complete all such maintenance and/or minor repair work whenever the nuclear reactor is placed in a shutdown mode in order to effect a refueling thereof. Included within the aforementioned work is any work of a maintenance or minor repair nature that needs to be done on the steam generator, and particularly on any of the internally housed components thereof. On the other hand, the accomplishment of such work should not interfere with the accomplishment of the refueling operation.
Under normal operating conditions, fluid flows through the interior of the steam generator. Consequently, before anyone can safely enter the interior of the steam generator to perform work therein, it is necessary that the fluid be drained therefrom. On the other hand, note is also taken of the fact that one of the steps that needs to be completed in the course of effecting the refueling of the nuclear reactor with which the steam generator is cooperatively associated involves the draining from the steam generator of the fluid, which during normal operations flows therethrough.
More specifically, to accomplish the refueling of the nuclear reactor, it is necessary to remove the head of the pressure vessel to expose the reactor core, which is housed in the vessel. However, before the head of the reactor pressure vessel can be removed, it is necessary to lower the level of the fluid, which for purposes of this discussion will be assumed to be water, that fills the interior of the pressure vessel. In actuality, the level of the water is lowered to a sufficient extent so as to be below the level whereat the head of the pressure vessel is joined to the pressure vessel. Even in its lowered state though, the level of the water is still sufficient to effect a covering of the reactor core. Because of the manner in which the steam generator is connected in fluid flow relation with the interior of the reactor pressure vessel, lowering the level of the water in the latter has the additional effect of draining the fluid, i.e., the water which otherwise flows to and through the interior of the steam generator.
After the head of the reactor vessel has been removed, it is once again necessary to flood the vessel with water. This is done in order to minimize the level of radiation to which the personnel that are engaged in the refueling operation are subjected. That is, the actual refueling of the reactor core is accomplished under water. Unfortunately, the aforesaid flooding of the pressure vessel has the concomitant effect of refilling the interior of the steam generator. Thus if personnel are to enter the interior of the steam generator to perform work therein while the refueling of the nuclear reactor is taking place, it is necessary to provide the inlet nozzle with a liquid tight seal while the steam generator is in a drained condition so as to block the flow, i.e., prevent water from reentering the steam generator when the pressure vessel is subsequently flooded following the removal of the head therefrom.
From the preceding discussion, it should be readily apparent that there exists a need to be able to effect a temporary blockage of the inlet nozzle and the outlet nozzle of the steam generator, i.e., to provide a liquid tight seal therein, while personnel are located in the steam generator performing work thereon. Furthermore, it has also been shown hereinabove that it is most desirable to be able to accomplish maintenance and/or minor repair work on the steam generator during those periods wherein the nuclear power generating system is in a shutdown mode. Finally, mention has also been made above of the fact that ingress to and egress from the interior of the steam generator by personnel having work to perform therein is accomplished through a means, such as a manhole, which is of limited dimension. Consequently, the blockage of the inlet nozzle and the outlet nozzle of the steam generator must be capable of being effected through the use of means, suitably dimensioned so as to be capable of being carried into the interior of the steam generator through the aforementioned manhole means.
One form of plug means, which has been employed heretofore in the prior art for purposes of effecting the temporary blockage of the inlet nozzle and/or the outlet nozzle of the steam generator has involved the usage of a diaphragm-like member designed to be suitably secured such as by means of a plurality of individual securing clamps, to a clamping ring. The inlet nozzle and the outlet nozzle each have such a clamping ring associated therewith. More specifically, there is one such clamping ring provided internally of the steam generator in juxtaposed relation to the inlet nozzle and another one located internally of the steam generator in juxtaposed relation to the outlet nozzle.
The above described form of plug means has not, generally speaking, been favorably received. There are a number of reasons for this. First of all, this form of plug means has proven to be susceptible to leaking. In many instances, the leaking has been found to be occasioned by the fact that it is difficult to achieve a liquid tight seal between the clamping ring and the diaphragm-like member. Namely, during periods of nonuse of the plug means, i.e., when the diaphragm-like member is not secured in place on the clamping ring, material becomes deposited on the surface of the clamping ring when the steam generator is in an operating mode, i.e., when fluid from the nuclear reactor is being circulated therethrough. Such material buildup on the clamping ring interferes with the accomplishment of a liquid tight seal between the diaphragm-like member and the clamping ring. Secondly, objections to the usage of this form of plug means have been raised on the part of some of the personnel, who have been assigned to work inside the steam generator with the subject plug means in place. By and large these objections have centered on two characteristics of this form of plug means; namely, the fact that the diaphragm-like member is secured on the clamping ring in such a manner that the fluid being blocked thereby exerts a force thereagainst tending to urge the diaphragm-like member out of engagement with the clamping ring, and the fact that the securing clamps are susceptible to being dislodged through the accidental engagement therewith by personnel working in the interior of the steam generator. Although the pressure of the fluid bearing against the plug means is not relatively high, the volume of fluid being blocked from entering the interior of the steam generator thereby would be sufficient to fill the interior of the steam generator, and thus in the event of a failure of the plug means would be sufficient to cause the drowning of any personnel caught within the steam generator when the plug means fails.
The above discussion should render it readily apparent that a need exists in the prior art for a plug means that would represent an improvement over known forms of plug means and for a plug means that would be particularly suited for employment for purposes of providing a temporary liquid tight sealing of the inlet nozzle and/or the outlet nozzle of a steam generator of the type that is designed to be cooperatively associated with a nuclear reactor in a nuclear power generating system of known construction. Moreover, such a plug means should embody dimensions enabling it to be carried into the interior of the steam generator through the same means, such as for instance a manhole, as that through which the steam generator interior is entered by personnel intending to work therein. Such a plug means should be further characterized by the fact that it can be secured in place within the time it takes to remove the head of the reactor vessel, and by the fact that the plug means after employment can be removed within the time it takes to replace the reactor vessel head. Preferably, such a plug means should be mountable in such a manner that the fluid being blocked thereby exerts a force thereagainst tending to urge the plug means into a blocking position. Lastly, such a plug means should be mountable in position relative to the inlet nozzle and/or the outlet nozzle of a steam generator in such a manner as to minimize the possibility of its being accidentally dislodged from its liquid tight sealing position by personnel working within the interior of the steam generator.
It is therefore an object of the present invention to provide a plug means of the type that is suitable for employment in a passage to effect the blockage of fluid therethrough.
It is another object of the present invention to provide such a plug means, which is particularly suited to be utilized for purposes of effecting a temporary liquid tight sealing of the inlet nozzle and/or the outlet nozzle of a steam generator, the latter being of the type employable with a nuclear reactor in a conventional form of nuclear power generating system.
It is still another object of the present invention to provide such a plug means, which can be readily disassembled so as to permit its passage through an opening of limited dimensions through which entry to the interior of the steam generator is normally effected.
A further object of the present invention is to provide such a plug means, which is readily capable of being secured in a blocking position relative to the inlet nozzle and/or the outlet nozzle of the steam generator within the time it takes to remove the head of the reactor vessel, and thereafter is capable of being removed from its blocking position within the time it takes to replace the head on the reactor vessel.
A still further object of the present invention is to provide such a plug means, which is capable of being mounted in a blocking position so as to effect a liquid tight sealing of the inlet nozzle and/or the outlet nozzle of the steam generator in such a manner as to render it relatively unlikely that the plug means will become accidentally dislodged by virtue of its being struck by personnel working within the interior of the steam generator.
Yet another object of the present invention is to provide such a plug means which is mountable in such a manner relative to the inlet nozzle and the outlet nozzle of the steam generator that the fluid being blocked thereby exerts a force thereagainst tending to urge the plug means into a blocking position.
Yet still another object of the present invention is to provide such a plug means that is relatively economical to manufacture, relatively easy to employ, and which is capable of providing reliable operation.